Summary of work: Alzheimer's disease (AD) is the most widespread among several neurological degenerative diseases (dementias) which occur principally at later ages, occasionally before 60, but more frequently after age 70. This study examines prospective psychological, neurological, and neuropsychological changes in participants from the Baltimore Longitudinal Study of Aging (BLSA). Neurological and neuropsychological examinations are administered to participants aged 60 and older, repeating many of the tests that were administered to these subjects at earlier ages. Diagnoses of probable Alzheimer's disease follow the NINCDS-ADRDA criteria. Estrogen replacement therapy (ERT) is increasingly recommended for post-menopausal women due to its beneficial effects on physical health in older women. Recent studies have suggested that ERT may have a protective effect on cognitive function and may reduce the risk for Alzheimer's Disease. We tested whether ERT had a protective effect on memory in nondemented women. Data on hormonal status and memory were examined in 288 postmenopausal women in the Baltimore Longitudinal Study of Aging. One hundred sixteen women who reported that they were receiving ERT during a cognitive assessment were compared with 172 women who had never received ERT. Women who were receiving ERT had fewer errors on the Benton Visual Retention Test (BVRT), a measure of short-term visual memory, visual perception and constructional skills. Furthermore, ERT appeared to protect against age changes in BVRT performance in a subgroup of 18 women for whom BVRT data were available prior to and during treatment with ERT. These findings suggest that ERT may protect against memory decline in nondemented postmenopausal women and offer further support for a beneficial role of estrogen on cognitive functioning in aging women. The effects of age and dementia on Trail Making Test (TMT) performance were investigated in a sample of 765 participants in the Baltimore Longitudinal Study of Aging, 58 of whom met DSM- IIIR criteria for dementia and 40 dementia 'suspects,' who showed mild changes in one or two cognitive domains. Cross- sectional analyses of 667 nondemented subjects showed significant age effects in completion times for both Parts A and B. Prevalence of errors increased with age on Part B, but not on Part A. Two-year longitudinal changes were examined in a subset of the sample (n = 385). Significant performance decrements for Part B, but not A, were found in completion times, with older age-groups showing the greatest slowing. These findings suggest that the effects of age and aging are greater on TMT Part B than Part A. Dementia status accounted for a significant proportion of the variance in completion times after accounting for age effects. ROC analyses suggest that the TMT may be useful in screening for cognitive dysfunction.